Resistive memory device, method of fabricating the same, and memory apparatus and data processing system having the same

ABSTRACT

A resistive memory device capable of implementing a multi-level cell, a method of fabricating the same, and a memory apparatus and data processing system including the same are provided. The resistive memory device includes a lower electrode, a first phase-change material layer formed over the lower electrode, a second phase-change material layer formed to surround an outer sidewall of the first phase-change material layer, and an upper electrode formed over the first phase-change material layer and the second phase-change material layer.

CROSS-REFERENCES TO RELATED APPLICATION

This application claims priority under 35 U.S.C. 119(a) to Koreanapplication number 10-2012-0093198, filed on Aug. 24, 2012, in theKorean Patent Office, which is incorporated by reference in itsentirety.

BACKGROUND OF THE INVENTION

1. Technical Field

The embodiments of the present invention relate to a semiconductorintegrated device, and more particularly, to a resistive memory device,a method of fabricating the same, and a memory apparatus and a dataprocessing system having the same.

2. Related Art

Dynamic Random Access Memories (DRAMs) operate at high speed, but theDRAMs are volatile. Flash memories are highly integrated andnonvolatile, but the flash memories may not guarantee operation speedequivalent to DRAM operation speed.

Studies on memory devices having advantages of the DRAMs and flashmemories have been actively progressed, and resistive memory devicesthat are nonvolatile and operate at a high speed have been suggested.

The resistive memory devices are a memory device using a variableresistive material, which switches at least two resistance states byrapid resistance change based on an applied voltage. There arephase-change RAMS (PCRAMs) and resistive RAMS (ReRAMs) memory devices asthe resistive memory devices.

The PCRAMs store data by changing a crystalline state of the variableresistive material with current applied to a heating electrode. ThePCRAMs have advantages of a nonvolatile property, high operation speed,stability, unnecessity of an erase operation, endurance, and support foraccess in units of bytes.

The PCRAMs have to be designed to support a multi-level cell (MLC)structure to obtain large capacity and high integration. The PCRAMshaving the MLC structure, which have been studied until recently, areimplanted using a method of controlling a pulse applied to memory cellshaving the same structure as a single-level cell (SLC).

That is, the current PCRAMs have to accurately control a pulse typeapplied to implement the MLC, and this is because a set/reset state ofdata becomes transited depending on crystallization of a phase-changematerial. When the property of the phase-change material is changed byrepetitive use of the PCRAMs, undesired data is written, and thus, thereare limitations to implement MLC through the same structure as SLC.

SUMMARY

In accordance with an embodiment of the present invention, the resistivememory device may include a lower electrode, a first phase-changematerial layer formed over the lower electrode, a second phase-changematerial layer formed to surround an outer sidewall of the firstphase-change material layer, and an upper electrode formed over thefirst phase-change material layer and the second phase-change materiallayer.

In accordance with another embodiment of the present invention, themethod of manufacturing a PCRAM device may include providing asemiconductor substrate in which a lower electrode is in formed,sequentially forming a first phase-change material layer, an electrodelayer, and a hard mask over the semiconductor substrate in which thelower electrode is formed, patterning the hard mask, the electrodelayer, and the first phase-change material layer so that the firstphase-change material layer is in contact with the lower electrode, anddoping and curing a preset combination element into the firstphase-change material layer to change an outer circumference of thefirst phase-change material layer to a second phase-change materiallayer having a predetermined thickness.

In accordance with another embodiment of the present invention, theresistive memory apparatus may include a memory cell array including aplurality of memory cells connected between word lines and bit lines,and a controller configured to control data write and data read for aselected memory cell in the memory cell array. Each of the plurality ofmemory cells may include a resistive device and a selection device. Theresistive device may include a lower electrode, first phase-changematerial layer formed over the lower electrode, a second phase-changematerial layer formed to surround an outer sidewall of the firstphase-change material layer, and an upper electrode formed over thefirst phase-change material layer and the second phase-change materiallayer.

In accordance with another embodiment of the present invention, the dataprocessing system may include a resistive memory apparatus, whichincludes a memory cell array including a plurality of memory cellsconnected to bit lines and word lines, each of memory cells including aresistive device and a selection device, and a controller configured tocontrol an operation of the memory cell array, and a memory controllerconfigured to access the resistive memory apparatus in response torequest of a host. The resistive device may include a lower electrode, afirst phase-change material layer formed over the lower electrode, asecond phase-change material layer formed to surround an outer sidewallof the first phase-change material layer, and an upper electrode formedover the first phase-change material layer and the second phase-changematerial layer.

In accordance with another embodiment of the present invention, the dataprocessing system may include a processor, an operation memoryconfigured to store an application, data, and a control signal requiredfor an operation of the processor, a resistive memory apparatus thatincludes a memory cell array including a plurality of memory cellsconnected to bit lines and word lines, each of memory cells including aresistive device and a selection device, and a user interface configuredto perform data input/output (I/O) between the processor and a user. Theresistive device may include a lower electrode, a first phase-changematerial layer formed on the lower electrode, a second phase-changematerial layer formed to surround an outer sidewall of the firstphase-change material layer, and an upper electrode formed over thefirst phase-change material layer and the second phase-change materiallayer.

These and other features, aspects, and embodiments are described belowin the section entitled “DETAILED DESCRIPTION”.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features and other advantages of thesubject matter of the present disclosure will be more clearly understoodfrom the following detailed description taken in conjunction with theaccompanying drawings, in which:

FIGS. 1 to 4B are views illustrating a method of fabricating a resistivememory device according to an exemplary embodiment of the inventiveconcept;

FIGS. 5 and 6 are line graphs illustrating operation characteristic of avariable resistive material applied to the inventive concept;

FIG. 7 is a block diagram illustrating a configuration of a memoryapparatus according to an exemplary embodiment of the inventive concept;

FIG. 8 is a block diagram illustrating a configuration of a dataprocessing system according to an exemplary embodiment of the inventiveconcept and

FIG. 9 is a block diagram illustrating a configuration of a dataprocessing system according to another exemplary embodiment of theinventive concept.

DETAILED DESCRIPTION

Hereinafter, exemplary embodiments will be described in greater detailwith reference to the accompanying drawings.

Exemplary embodiments are described herein with reference tocross-sectional illustrations that are schematic illustrations ofexemplary embodiments (and intermediate structures). As such, variationsfrom the shapes of the illustrations as a result, for example, ofmanufacturing techniques and/or tolerances, are to be expected. Thus,exemplary embodiments should not be construed as limited to theparticular shapes of regions illustrated herein but may be to includedeviations in shapes that result, for example, from manufacturing. Inthe drawings, lengths and sizes of layers and regions may be exaggeratedfor clarity. Like reference numerals in the drawings denote likeelements. It should be readily understood that the meaning of “on” and“over” in the present disclosure should be interpreted in the broadestmanner such that “on” not only means “directly on” something but alsoinclude the meaning of “on” something with an intermediate feature or alayer therebetween, and that “over” not only means the meaning of “over”something may also include the meaning it is ‘over’ something with nointermediate feature or layer therebetween (i.e., directly onsomething).

FIGS. 1 to 4B are views illustrating a method of fabricating a resistivememory device according to an exemplary embodiment of the inventiveconcept.

First, a first phase-change material layer 103, electrode layers 105 and107 and a hard mask 109 are sequentially formed on a semiconductorsubstrate 101 in which a bottom structure is formed.

An access device and a lower electrode may be formed in thesemiconductor substrate 101, and a word line may be further formed onthe semiconductor substrate 101. The bottom structure may be designedusing various types and methods and is beyond the scope of the inventiveconcept, and thus, detailed description thereof will be omitted.

The electrode layers 105 and 107 may have a stacked structure of atitanium layer 105 and a titanium nitride layer 107, but the electrodelayers are not limited to the stacked structure.

The first phase-change material layer 103 may be selected from amaterial in which a crystalline state is changed based on the appliedcurrent. For example, the first phase-change material layer 103 may beformed using a binary chalcogenide compound, for example, germanium(Ge)-tellurium (Te).

Referring to FIG. 2A, the hard mask 109 is patterned using a photoresistfilm (not shown) and then, the electrode layers 107 and 105 and thefirst phase-change material layer 103 are patterned using the patternedhard mask as an etch mask. At this time, the patterned structure may beformed to have a cylindrical shape of cross-section, but the patternedstructure is not limited thereto.

Through the patterning process, a top of the first phase-change materiallayer 103 is shielded by the electrode layers 105 and 107 and the hardmask 109, a bottom thereof is shielded by the semiconductor substrate101, and thus only sides thereof are exposed.

FIG. 2B illustrates a layout diagram after the process of FIG. 2A iscompleted.

Referring to FIG. 3, a preset combination element 111 is doped into thesemiconductor substrate 101 in which the patterned structure is formed.The combination element 111 may be selected from a material, which ischemically combined with a component of the first phase-change materiallayer 103, to represent resistance change characteristic. If the firstphase-change material layer 103 includes, for example, Ge—Te, thematerial that is chemically combined with Ge—Te to represent theresistance change characteristic may be antimony (Sb).

In FIG. 3, the combination element 111 to be combined with the firstphase-change material layer 130 may be doped using a plasma doping(PLAD) method and controlled to be isotropically doped. At this time,materials (the hard mask 109 and the electrode layers 105 and 107) otherthan the exposed surface of the first phase-change material layer 103are amorphous, and thus, the combination element 111 is not well dopedinto the amorphous material. Therefore, the selective doping only intothe sidewall of the first phase-change material layer 103 is possible.

The doping energy is controlled so that the combination element 111 isdoped only into the sidewall of the first phase-change material layer103 and therefore, a phase-change material pattern is to be formed in acore-shell structure in a subsequent process.

A cleaning process for removing the combination element 111 doped in anundesired portion is performed and then a low temperature curing processfor stabilizing the combination element 111 is performed. Therefore, asshown in FIG. 4A, a second phase-change material layer 113 is formed tosurround the sidewall of the first phase-change material layer 103.

FIG. 4B illustrates a plan view of the resistive memory deviceillustrated in FIG. 4A, wherein FIG. 4B illustrates a plan viewillustrating a portion in which the first and second phase-changematerial layers 103 and 113 are formed.

As shown in FIG. 4B, the first phase-change material layer 103 is formedin a center position, that is, in a core. The first phase-changematerial layer 103 is in contact with the lower electrode (not shown),and thus is changed in the crystallization state by the heat appliedthrough the lower electrode. The second phase-change material layer 113may be formed in a shell surrounding an outer circumference of thecenter position.

On the other hand, a thickness of the second phase-change material layer113 may be determined based on a process parameter in the curing processand composition of the second phase-change material layer 113 may bealso determined. The thickness and composition of the first and secondphase-change material layers 103 and 113 may be parameters forimplementing the MLC, and therefore, the MLC may be fabricated throughonly simple change of the process parameter for determining a curingcondition in the inventive concept.

In the resistive memory device as formed, the first phase-changematerial layer 103 formed in the core and the second phase-changematerial layer 113 formed in the shell have electric properties fromeach other.

If the first phase-change material layer 103 is formed of Ge—Te, thesecond phase-change material layer 113 may include germanium(GO-antimony (SW-tellurium (Te) (GST) using Sb as the combinationelement 111. Ge—Te has a high melting point and low crystallizationspeed compared to GST. Therefore, the MLC may be implemented using theelectric property difference.

FIGS. 5 and 6 are views illustrating operation characteristic of avariable resistive material applied to the inventive concept.

First, FIG. 5 illustrates voltage-current characteristic of the GSTmaterial and the Ge—Te material. It can be seen from FIG. 5 that the GSTmaterial A1 has lower resistance compared to the Ge—Te material B1.

FIG. 6 is a graph illustrating resistance change when a write current isapplied to the GST material A2 and the Ge—Te material B2. In can be seenfrom FIG. 6 that the resistance change in the Ge—Te material B2 easilyoccurs even in the low write current while the GST material A2 needshigher write current than the Ge—Te material B2.

Actually, the Ge—Te material has a melting point of 725° C. in a bulkstate and the GST material has a low melting point of 616° C. As shownin FIGS. 5 and 6, the crystallization state in the Ge—Te material ischanged in lower current than the GST material according to the meltingproperty. Therefore, the melting property is applied to the ReRAM toenable the MLC to be implemented.

The phase-change material layer may include a GST single layer in thegeneral phase-change memory device. Therefore, only two states of thecrystallization state and the amorphous state in the GST material areused as a data storage property. Thus, precise current control isnecessary to implement MLC in the general PCRAM including the GST singlelayer.

However, in the PCRAM of the exemplary embodiment, the phase-changematerial layer is formed in the core-shell structure and in particular,the phase-change material layer in the core includes a material having amelting point higher than the phase-change material layer in the shell.A heating electrode may be in contact only with the phase-changematerial layer in the core, and thus, resistance state of thephase-change material layer in the shell is changed by the heatconducted from the phase-change material layer in the core.

That is, the phase-change material layer is formed by the core-shelldual structure having different electric properties from each other toeasily control the resistance state, and thus, MLC may be implemented.

FIG. 7 is a view illustrating a configuration of a memory apparatusaccording to an exemplary embodiment of the inventive concept.

Referring to FIG. 7, a memory apparatus 300 according to the exemplaryembodiment of the inventive concept includes a memory cell array 310, adecoder 320, a read/write circuit 330, an input/output (I/O) buffer 340,and a controller 350.

Each of a plurality of memory cells included in the memory cell array310 may be configured to include the resistive memory device illustratedin FIG. 4A. Furthermore, the plurality of memory cells in the memorycell array 310 are connected to the decoder 320 through a word line WL.The plurality of memory cells in the memory cell array 310 are alsoconnected to the read/write circuit 330 through a bit line BL.

The decoder 320 receives an external address ADD and decodes a rowaddress and a column address to be accessed in the memory cell array 310by control of the controller 350, which operates according to a controlsignal CTRL.

The read/write circuit 330 receives data DATA from the I/O buffer 340and writes data in a selected memory cell of the memory cell array 310under the control of the controller 350 or provides data read from aselected memory cell of the memory cell array 310 to the I/O buffer 340under the control of the controller 350.

FIG. 8 is a block diagram illustrating a configuration of dataprocessing system according to an exemplary embodiment of the inventiveconcept.

A data processing system 400 illustrated in FIG. 8 may include a memorycontroller 420 connected between a host and a resistive memory apparatus410.

The memory controller 420 may be configured to access the resistivememory apparatus 410 in response to request of the host, and thus, thememory controller 420 may include a processor 4201, an operation memory4203, the host interface 4205, and a memory interface 4207.

The processor 4201 may control an overall operation of the memorycontroller 420, and the operation memory 4203 may store an application,data, a control signal, and the like, required for operation of thememory controller 420.

The host interface 4205 performs protocol conversion for exchange ofdata/control signal between the host and the memory controller 420. Thememory interface 4207 performs protocol conversion for exchange ofdata/control signal between the memory controller 420 and the resistivememory apparatus 410.

The resistive memory apparatus 410 may include a memory cell arrayconfigured of unit memory cells each including a resistive device, inwhich the variable resistive material is formed between two electrodelayers, and a selection device. In particular, the resistive device maybe a resistive device using a first phase-change material layer formedin a center position thereof and a second phase-change material layerformed to surround an outer circumference of the first phase-changematerial layer as a variable resistive material layer.

In the exemplary embodiment of the inventive concept, the dataprocessing system illustrated in FIG. 8 may be a memory card, but thedata processing system is not limited thereto.

FIG. 9 is a view illustrating a configuration of a data processingsystem according to another exemplary embodiment of the inventiveconcept.

A data processing system 500 illustrated in FIG. 9 includes a resistivememory apparatus 510, a processor 520, an operation memory 530, and auser interface 540. If necessary, the data processing system 500 mayfurther include a communication module 550.

The processor 520 may be a central processing unit (CPU), and theoperation memory 530 may store an application program, data, a controlsignal, and the like, required for an operation of the data processingsystem 500. The user interface 540 provides an environment accessible tothe data processing system 500 by the user and provides a dataprocessing procedure, result, and the like of the data processing system500 to the user.

For example, the resistive memory apparatus 510 may include a memorycell array configured of unit memory cells each including a resistivememory device illustrated in FIG. 4A and a selection device. Inparticular, the phase-change material layer included in the resistivedevice may include a first phase-change material layer formed in acentral portion thereof and a second phase-change material layer formedto surround an outer circumference of the first phase-change materiallayer.

On the other hand, the data processing systems illustrated in FIGS. 8and 9 may be used as a disc apparatus, a built in/external memory cardof a mobile electronic apparatus, an image processor, and otherapplication chipsets.

The above embodiments of the present invention are illustrative and notlimitative. Various alternatives and equivalents are possible. Theinvention is not limited by the embodiment described herein. Nor is theinvention limited to any specific type of semiconductor device. Otheradditions, subtractions, or modifications are obvious in view of thepresent disclosure and are intended to fall within the scope of theappended claims.

What is claimed is:
 1. A resistive memory device, comprising: a lowerelectrode; a first phase-change material layer formed over the lowerelectrode; a second phase-change material layer formed to surround anouter sidewall of the first phase-change material layer; and an upperelectrode formed over the first phase-change material layer and thesecond phase-change material layer, wherein the second phase-changematerial layer is configured to have lower resistance than the firstphase-change material.
 2. The resistive memory device of claim 1,wherein the first phase-change material layer includes a material havinga higher melting point than the second phase-change material layer. 3.The resistive memory device of claim 1, wherein the first phase-changematerial layer includes a germanium-tellurium (Ge—Te) compound.
 4. Theresistive memory device of claim 3, wherein the second phase-changematerial layer includes a germanium-antimony-tellurium (Ge—Sb—Te)compound.
 5. The resistive memory device of claim 1, wherein the firstphase-change material layer has a cylindrical shape.